A procedure known as balloon valvuloplasty is used to treat calcified, stenotic heart valves. In this procedure, a catheter having a deflated balloon is inserted through a vein or artery into the heart until the balloon is within the heart valve to be treated. The balloon is then inflated to dilate the diseased valve. After dilation, the balloon is deflated and withdrawn from the cardiovascular system of the patient.
Currently, this procedure is performed with large diameter, conventional polyethylene balloon dilator catheters. In order to be large enough to dilate a heart valve, the balloon must have a relatively large diameter when inflated. On the other hand, in order to be able to advance the catheter and balloon through a vessel of the patient to the heart, it must present a small diameter profile when deflated. To accommodate both of these requirements, the conventional dilator catheter has a balloon of large diameter which is prefolded prior to insertion into the vessel to make the cross section smaller so that the balloon can be advanced through the vessel to the heart.
Carrying out of the balloon valvuloplasty procedure with this kind of dilator catheter creates a number of problems. For example, the folds in the balloon form, in effect, radially extending wings or webs which tend to cause trauma and bleeding during withdrawal of the catheter. In addition, the large diameter folded balloon occupies an undesirably large portion of the cross-sectional area of the vessel during insertion and withdrawal of the catheter.
The radial dimensions of the balloon must increase substantially when inflated in order that the balloon can be small enough to pass through a vessel leading to the heart and be large enough in the inflated condition to dilate a heart valve. For this reason, it is not possible to safely use a conventional distensible latex balloon because of the likelihood that the elastic limit of the balloon would be exceeded.
One kind of nephrostomy catheter and a catheter for dilating blood vessels use a balloon which is radially expandable and axially contractable. However, these balloons are not able to radially expand to the relatively large diameter necessary to dilate a heart valve, and they have an abrupt change of stiffness within the balloon which would be undesirable for treating heart valves.